This invention relates to an improved flexible dummy bar used in continuous casting equipment. Examples of dummy bars and their use are disclosed in U.S. Pat. No. 3,442,322 issued May 6, 1969 to Lemper and U.S. Pat. No. 3,581,808 issued June 1, 1971 to Vertesi and Phillips.
In the conventional continuous casting process for producing continuous strand or slab from steel and the like, molten metal is poured into the open top of a mold which also has an open bottom. The metal solidifies against the cooled interior walls of the mold to form a solidified skin surrounding a molton core. The solidifying strand emerges from the lower end of the mold and is guided away from the mold. From the time the strand leaves the mold, cooling continues so that the core ultimately solidifies. Then, the strand is cut to lengths for further processing.
The conventional process involves gravity pouring the molten metal downwardly into the open upper end of the mold, withdrawing the partially solidified strand downwardly, and gradually curving the strand along an arc until it continues in a horizontal direction for cutting. The movement of the strand along the arc involves guiding the strand with appropriate rollers. The above mentioned patents illustrate the strand movement and the general procedure involved.
When the casting operation begins, the lower end of the mold must be temporarily plugged to prevent the molten metal from simply running through it. That is, the molten metal must be retained within the mold for a sufficient period of time to begin the solidification. Thereafter, the plug can be removed.
Conventionally, the types of plugs used are positioned within the mold and held in place by a "dummy bar". This is an elongated strip having an end fastened to the mold plug. The strip extends between the rollers used to guide and pull the strand which exists from the mold. An endwise pulling force on the dummy bar withdraws the plug from the mold and moves the plug along the arcuate path. Since, the lead end of the strand interlocks with the plug, the strand follows the plug and dummy bar movement along the arcuate path.
In general, prior dummy bars comprise an elongated strip that can be bent into an arcuate curve while the dummy bar is pulled longitudinally for pulling and guiding the plug with the attached lead end of the cast strand. Such strips are formed of interconnected sections. Thus, because of manufacturing tolerances, looseness of connection means, etc., there is an inherent, limited, relative movement between bar sections. This presents a problem.
Ordinarily, the plug is held within the mold by a generally vertically arranged portion of the dummy bar. Consequently, that portion of the dummy bar acts like a support column upon which the plug rests. Hence, the weight of the plug, along with the weight of the incoming molten metal, comprises the dummy bar downwards. This presses the dummy bar sections rigidly together to eliminate looseness at connections. However, when the dummy bar is pulled longitudinally, the usual tolerances or spaces between the sections and their connections cause a momentary expansion or elongation of the dummy bar until the dummy bar sections stabilize in their longitudinal movement. The effect is similar to a railroad engine pulling a train from a stationary start.
The rapid momentary elongation of the dummy bar permits the plug to suddenly drop down a short distance. That drop can cause rupturing of the still thin, solidifying skin on the strand to produce a "breakout" or release of the molten core through the solidified skin.
Consequently, it is desired to have a dummy bar which does not change length when pulled despite having the usual tolerances or looseness inherent in manufacturing a large, elongated, multiple part device of this kind. The invention herein relates to such an improvement in dummy bar construction, i.e., one wherein the bar is flexible to a limited degree for guiding the plug and strand around a curve, but nevertheless, which does not change length or become loose in endwise movement in either direction.